Recovery of a vaporizable hydrocarbon from liquid mixtures



Jan. 5, 1960 w, POLLOCK- ETAL 2,920,113

RECOVERY 0F A VAPORIZABLE HYDROCARBON FROM LIQUID MIXTURES Filed July27, 1956 RECOVERY OF A VAPORIZABLE yIIYDROCARBON FROM LIQUID Lyle w.Pollock, Alvin J. Andrews, and Edward N. Pennington, Bartlesville,Okla., assgnors to Phillips Petroleum Company, a corporation of DelawareApplication Jnly 27, 19'56, serinl Nn. 600,626

- 12 claims. (1.260-655) butadiene, and the like, and a compoundpolymerizable.

therewith contains an active CH2=C group such as styrene, acrylonitrile,methyl methacrylate, and the like,l

to produce a synthetic elastomer, unreacted monomers are usually presentin the latex. whether employing the cold rubber polymerization processor an `older higher temperature copolymerization process. When utilizingeither of these processes for the production of synthetic elastomers,themonomers not converted in the polymerization reaction are usuallyrecovered from the reaction mixture by vacuum recovery. As is well knownin vacuum processes, it is very difficult to lexclude all traces ofatmospheric oxygen and the recovered monomers from the vacuumv recoverystepsgenerally will contain intolerable quantities of free oxygen.Because the contaminating oxygen originates from the atmosphere, theoxygencontaminated monomers usually also contain free nitrogen. n

Ithas been found that oxygen dissolved in the mono mers noted abovemarkedly aiects the rate of polymerization of these materials.Generally, in a cold rubber process the oxygen is not permitted toexceed parts per million. It has also been found that varyingconcentrations of dissolved oxygen in,'for example, butadiene, and/ orstyrene, cause the rates of polymerization to vary. Thus, it is diicultto determine whether a batch of butadiene and styrene will copolymerizeat the normally expected rate or will copolymerize more rapidly or moreslowly than the desired rate. When rates of reaction vary, it is diicultto control the temperature of the reaction and the extent of conversion.The copolymerization reaction is exothermic and too rapid a rate ofreaction `tends to increase the temperature of the system. In theproduction of cold rubber, it is especially important to maintain thetemperature of the polymerization reaction and the extent of conversion,within relatively narrowlimits.

' .Accord-ingly, one or more of the following objects will beobtained bythe practice of our invention.

l An object of this invention is to provide a method for recovering aneasily vaporizable hydrocarbon from liquid mixtures containing same.

-*Another object of this invention is to provide a novel method forpurifying a monomer containing a xed gas impurity. l g

Svtill another .object is to recover butadiene containing a low freeoxygen gas content.

` A- further object is to provide a process' which is relativelyeconomical and elcient, and wherein the equipnient requirements arefulfilled in a novel and advantage- 9.1.15. mar. I

This condition exists Iiatented .Jam 5, -1960 rnice.

Numerous other objects ofthe presentiinvention will be apparent to thoseskilled in the art from a consideration of the specication'taken inconjunction with the accompanying drawing. v

Broadly,our invention comprises a process of recovering an easilyvaporizable hydrocarbon from liquid mixtures by first separating asubstantial portion of 'said vaporizable hydrocarbon, in a rstseparation zone, introducing the liquid effluent containing theremainder of said vaporizable hydrocarbon -to a second separation zone,such as a vacuum ilash zone, wherein the remainder of the vaporizablehydrocarbon containing a'tixed gas im,-l purity is substantiallyrecovered and passed in contactv sure at least atmospheric; theresulting emulsion polymerizate containing minoror residual amounts ofmonomer is introduced into a flash zone maintained at sub-at-A mosphericpressure wherein the remainder of the monomer together with free oxygenimpurity and other gases `originating from the atmosphere (which haveleaked into the vacuum operation) are recovered-asa gaseous stream.`

and said stream is passed in contact with a liquid absorbent mediumwhich preferentially absorbs the mono-A meric material. Free oxygen,nitrogen,-etc., are vented from `the absorption zone, and the enrichedabsorbent medium is stripped to recover the monomer therefrom.

The absorbent liquids which are applicable in our invention are a heavynaphtha oil, mineral seal oil, kerosene, light gas oil, furfural, andothers known in the art. In general, narrow boiling range hydrocarbonfractions between the hexane and gasoil ranges are applicable, such as akerosene fraction.V The primary requirement is that the absorbent mediummust possess a preferential solubility for the hydrocarbon to berecovered. In addition, the absorbent liquid must possess a relativelylow volatility so that it is not lost overhead in the absorption andstripping zones; moreover, it is desirable not to employ an absorptionliquid which has a relatively high boiling range since the bottomstemperature in the stripping zone would tend to rise, thus creating theproblem of `diolefn polymerization. Absorbent liquids such as mineralseal oil, furfural, kerosene, and the like are examplesof applicableabsorber media for our process.

Better understanding of our process will be obtained upon reference tothe accompanying diagram which 'discloses one embodiment of theinvention. The gure portrays diagrammatically one arrangement ofequipment which lcan advantageously be employed when carrying out theinstant invention.A lAuxiliary apparatus such' as pressure andtemperature indicating, recording and control equipment, various valves,pumps, etc., are not shown in the gure for simplicity and brevitypurposes. The need for such apparatus, its installation and oper-lation, are well understood by those skilled in the'art.

Referring then to the drawing, reference numeral 11 identities a conduitthrough which latex passes from a butadiene-styrene copolymer plantintol separation zone 1,2 which is operated at a temperature ofapproximately F. and a pressure of approximately 1Z0V p.s.i.a.substantial 'portion' of vaporcus' butadiene plu'sa small butadiene,pentadiene, isoprene, chloroprene,`

quantity of styrene is covered from the latex and is passed overhead viaconduit 13 and into foam trap 14 wherein a portion of thebutadiene-containing material is recycled back to the separation zone12. Vaporous butadiene in conduit 16 is introduced into the primarybutadiene compressorflT;through cooler 18, and into butadiene receiver19. Water is removed from thebutadiene receiver by pipe 21 and vaporousbutadieneA isV taken overhead and through a pressure relief valve inconduit 20 to be treatedas'described -hereinbelow. Liquid butadiene,including a small quant-ity of styrene is removed via conduit 22 andraportion-'thereof is` introduced into the butadiene-styrene fractionator24 by line 23; the remaining portion is diverted through conduit 36 tovessel 37. The particular division of stream 22 will ydepend upon thequantity of -butenes and/or other impurities (if any) present inthestream 22 which will be removed in a puritication step, not shown. Y AVpolymerization inhibitor can be introduced at 40 into stream 23.Vaporous butadiene is taken overhead from the butadiene-styrenefractionator24 in conduit 25, through cooler 26 and intoV refluxaccumulator 27. The temperature at the top of the fractionator is 102 F.while the bottoms temperature is maintained at 150 F. The pressure is 65p.s.i.a. Liquid butadiene is removed from the reiiux accumulator 27 viaconduit 28 wherein a portion is recycled to fractionator 24 as refluxand the remainder is passed via conduit 29 to a purification recoverystage wherein butenes and/ or other impurities are removed (not shown).Liquid styrene and small quantities of butadiene are recovered aslbottoms product from fractionator 24 via conduit 31 where a portionthereof is recycled through reboiler 32 to the fractionation zone andthe remainder thereof is introduced into vacuum ash zone 33. Vaporousbutadiene is taken overhead from zone 33 to be treated as hereinafterdescribed. Liquid styrene and higher boiling materials are removedfrom-'zone 33 by pipe Y35 for further processing, not show.

Referring back to the first separation zone 12, liquid eiuent containinglatex, unreacted styrene monomer, and residual butadiene monomer are.removed from zone 12 via conduit 41 and introduced into vacuum flashzone 42. The temperature in said vacuum liash zone 42 is approximately90 F. and the pressure is about 180` mm. mercury. Residual vaporousbutadiene containing free oxygen and nitrogen is removed overhead bypipe 43k and introduced into foam trap 44 wherein a portion of thecontents in foam trap 44 is recycled to zone 42. Latex containingsubstantial ,quantities of unreacted styrene is removed from vacuumflash zone 42 by conduit 46 to be further processed in means not shown.Steam jet ejector 48 is employed to maintain the vacuum in flash zone42. Vaporous butadiene, and free oxygen and nitrogen are removed fromfoam trap 44 via conduit 47, and together with vaporous butadiene fromconduit 34 the total efuent is passed through steam jet ejector 48 intocooler 51 and subsequently into knock-out drum 52. A water phase isremoved via conduit 53 and vaporous butadiene containing Vfree oxygen,nitrogen, etc., is taken overhead via conduit 54. Vaporous butadienefrom conduit 2t) and conduit 92 (to be discussed hereinafter) isintroduced into conduit 98 and the total effluent in conduits 98 and 54are passed to compressor 56 and subse-v quently to packed tower 57.kLiquid butadiene is recovered as bottoms -fromtower 57 via conduit 96and is passed to ash zone 97., `Vaporous butadiene is removed overheadvia conduit 9,8 which is connected to conduit 54. Liquid butadiene istaken from ash zone 97 via conduit 99 and isrecycledito conduit 11'.Vaporous butadiene is removed overhead from tower 57 viaY pipe 58through cooler 59 and into accumulator, 61. A portion of the liquidbutadiene' in accumulator 61 is recycled to the upper section' of packedtower Y57 while vaporous butadiene, free oxygen, nitrogen, etc., vare,removed from` accumulata 61V by'ppe. 62 andrai-*wanted me theiower 4 Y.section of absorber 63 to lcounter-'current contact with a heavy naphthaoil, introduced via conduit at the upper section of the absorptioncolumn. The temperature at the upper portion of the absorption zone isF.. and the bottoms temperature is held at approximately F.; thepressure is 110 p.s.i.a. The heavy naphtha oil selectively absorbs the`unreacted butadiene monomer, and the enrichedheavy naphtha oil isremoved fromA v the bottom of absorber 63 via conduit 66,. through heatlexchanger 67, and is introduced into stripper 68, said stripper` beingheld at a kettle temperature of 265 F.v and a top temperature o,f.49,F.at a pressure of 20 p.s.i.'a. Free nitrogen, oxygen, and' normallygaseous hydrocar bon impurities are vented ,from the absorption systemthrough conduit 64. In stripper 68 (a fractionating column) the absorbedbutadiene is recovered from the enriched heavy naphtha oil and is takenoverhead in a va porous state via conduit 81, compressor 82 and cooler'83, and isV introduced into accumulator 84. v Lean heavy naphtha oil isrecovered as bottoms product from stripf per 68, a portion thereof ispassed through conduit 78' into reboiler 79 and recycled to the lowersection of the stripping zone. A second stream of the lean heavy naphthaoil is taken viaconduit 71, through heat exchanger 67, and is introducedinto surge tank 72 wherein water is removed therefrom through conduit73. The lean absorber oil from surge tank 72 is passed via conduit 74,through cooler 76,to the upper portion of absorber 63 to again be usedin the absorption step. Make-up heavy naphtha oil is introduced viaconduit 80. In ac# cumulator 84, water is removed therefrom via conduit'87 and liquid butadiene via conduit 86for reflux to strip' per 68.Liquid butadiene is introduced into flash zone' 89 via conduit 8 8.Vaporous butadiene from accumula# tor 84 and flash zone 89 is takenoverhead to further reduceV oxygen content of v91 and the combinedstreams are recycled via conduit 92 to conduit 20. Liquid buta#l dieneis recovered from ash zone 89 via conduit 91. and is introduced intovessel 37. Liquid butadiene is' removed from vessel 37 by conduit 38 forrecycle to the emulsion polymerization process, not shown.

The following tabulation sets forth the operating conditions oftemperature and pressure maintained in various parts of the embodimentdescribed in the figure.

A feed stream comprising the reactor effluent from a butadiene-styreneemulsion copolymerization process; is introduced into separation zone12. This stream contains 62,580 pounds per day of unreacted butadiene,together ywith styrene, water, polymer and the variousY otheringredients present in the polymerization recipe. Flashing of thisstream `in zone 12 results in the removal of 50,064 pounds per day ofbutadiene overhead in line 13. This stream is passed, after compressionand cooling, to receiver 19.v Butadiene is Withdrawn from re ceiver19via line 22, about'44 percent Yof the stream in' line 22 being passedto butadiene-styrene fractionator 24 for the removal of. the smallamount of styrene con-` tained therein. Butadiene taken overhead fromfractionator 24 is passed via line 29 to further purification (notshown). The remainder of the stream in line 22v is passed via line 36 tovessel 37 from which it is recycled to the polymerization reactor. Theoxygen cona tent of the butadiene in line 36 is about 1.4 p.p.m. (partsper million).

The liquid stream removed from zone 12 via line 41, containing about12,516 pounds per day of butadiene is vacuum ashed in zone 42, butadienebeing removed overhead therefrom via line 43 at a rate of about 10,013

pounds per day. This latter stream is treated in absorber 63 for theremoval therefrom of air, especially oxygen, unavodably introduced invacuum ash zone 42. The major portion of the air is vented from thesystem via line 64. The thus purified butadiene, the overhead productfrom stripper 68, is ashed in zones 84 and 89 and the liquid phase fromthis ash zone is passed via line 91 to vessel 37. The oxygen content ofthis stream has been reduced to 33 p.p.m. by the flashing and absorptionand stripping operations. The combined recycle butadiene stream in line38, including that from both lines 36 and 91, is found to contain onlyabout 6.5 p.p.m. of oxygen.

Thus, it is seen that by the process of this invention, the recovery ofunreacted butadiene is effected in an efficient manner by a combinationof tiashing steps, and that only a small proportion of the recoveredbutadiene (less than 20 percent) becomes contaminated with oxygen andrequires removal of the oxygen by the method described in thisapplication.

It will be apparent that various modifications of the invention can bemade upon study of the accompanying disclosure without departing fromthe spirit and scope of said disclosure.

We claim:

1. A method of recovering an aliphatic conjugated diene from a latexmixture which comprises introducing said latex into a separation zonemaintained at a pressure of at least atmospheric, recovering asubstantial portion of said aliphatic conjugated diene as a firstvaporous overhead stream from said separation zone, introducing thelatex etliuent from said separation zone to a flash zone maintained atsub-atmospheric pressure, recovering a second vaporous overhead streamcomprising aliphatic conjugated diene and free oxygen gas, introducingsaid second stream into an absorption zone to contact with an absorptionsolvent, said absorption solvent selectively extracting said aliphaticconjugated diene, removing overhead unabsorbed gases comprising freeoxygen gas from the absorption zone, and recovering said aliphaticconjugated 'diene from said absorption solvent.

2. The method of claim 1 wherein said aliphatic conjugated diene is1,3-butadiene.

3. The method of claim 1 wherein said aliphatic conjugated diene ispiperylene.

4. The method of claim 1 wherein said aliphatic conjugated diene ischloroprene.

' 5. The method of claim 1 wherein said aliphatic conjugated diene ismethylpentadiene.

6. The method of claim 1 wherein said aliphatic conjugated diene is2,3-dimethyl-1,3-butadiene.

7. A methodl of purifying butadiene containing a fixed gas impuritywhich comprises introducing a butadienecontaining latex stream into aseparation zone maintained at a pressure of at least atmospheric,removing overhead a vaporous efuent comprising a substantial portion ofbutadiene and a minor portion of styrene, condensing said overheadeffluent, introducing a portion of said condensed euent to afractionation zone, withdrawing overhead a product comprising butadieneand withdrawing a bottoms product comprising styrene and smallquantities of butadiene from said fractionation zone, and recoveringsaid butadiene from said fractionation bottoms; removing a latex eiuentfrom said separation zone and passing same to a ash zone maintained atsub-atmospheric pressure, recovering overhead a vaporous streamcomprising butadiene and a ixed gas impurity from said ash zone,introducing last mentioned overhead stream into an absorption zone tocontact with an absorption solvent, said absorption solvent selectivelyextracting butadiene, removing unabsorbed gases comprising said fixedgas impurity from said absorption zone, and recovering butadiene fromthe enriched absorption solvent.

8. The method of claim 7 wherein said fixed gas impurity is oxygen.

9. The method of claim 8 wherein the absorption Asolvent is mineral sealoil.

10. The method of claim 8 wherein the absorption solvent is furfural.

1l. The method of claim 8 wherein the absorption solvent is a kerosenefraction.

12. The method of claim 8 wherein the absorption solvent is a gas oil.

References Cited in the tile of this patent UNITED STATES PATENTS2,415,006 Hachmuth Jan. 28, 1947 2,506,065 Clark May 2, 1950 2,556,851Ohsol et al. June 12, |951 2,666,042 Nozaki Jan. 12. 1954

1. A METHOD OF RECOVERING AN ALIPHATIC CONJUGATED DIENE FROM A LATEXMIXTURE WHICH COMPRISES INTRODUCING SAID LATEX INTO A SEPARATION ZONEMAINTAINED AT A PRESSURE OF AT LEAST ATMOSPHERIC, RECOVERING ASUBSTANTIAL PORTION OF SAID ALIPHATIC CONJUGATED DIENE AS A FIRSTVAPOROUS OVERHEAD STREAM FROM SAID SEPARATION ZONE, INTRODUCING THELATEX EFFLUENT FROM SAID SEPARATION ZONE TO A FLASH ZONE MAINTAINED ATSUB-ATMOSPHERIC PRESSURE, RECOVERING A SECOND VAPOROUS OVERHEAD STREAMCOMPRISING ALIPHATIC CONJUGATED DIENE AND FREE OXYGEN GAS, INTRODUCINGSAID SECOND STREAM INTO AN ABSORPTION ZONE TO CONTACT WITH AN ABSORPTIONSOLVENT, SAID ABSORPTION SOLVENT SELECTIVELY EXTRACTISNG SAID ALIPHATICCONJUGATED DIENE, REMOVING OVERHEAD UNABSORBED GASES COMPRISING FREEOXYGEN GAS FROM THE ABSORPTION ZONE, AND RECOVERING SAID ALIPHATICCONJUGATED DIENE FROM SAID ABSORPTION SOLVENT.